API v2 - You specified an invalid image for Droplet creation.

As you read the title when i make request with PHP cURL i get the response message of invalid image.

I can see all the image listings "/v2/images/" including the one i request with JSON data which looks like this:
<pre>
{
"name": "My-Droplet",
"region": "nyc1",
"size": "4gb",
"image": 4201396
}
</pre>
Now the image 4201396 is totally exist and I also able to get image details "/v2/images/4201396".

Why the droplet creation API method didn't recognize the image id? How can i prevent the error? And why the error occurred?

I'm also having this same issue. I've tried using both a slug as a string and an image id as a number when posting to the API. I'm also only using regions where the image is available. Any idea what's going on?